2,242 research outputs found
An Asymptotically-Optimal Sampling-Based Algorithm for Bi-directional Motion Planning
Bi-directional search is a widely used strategy to increase the success and
convergence rates of sampling-based motion planning algorithms. Yet, few
results are available that merge both bi-directional search and asymptotic
optimality into existing optimal planners, such as PRM*, RRT*, and FMT*. The
objective of this paper is to fill this gap. Specifically, this paper presents
a bi-directional, sampling-based, asymptotically-optimal algorithm named
Bi-directional FMT* (BFMT*) that extends the Fast Marching Tree (FMT*)
algorithm to bi-directional search while preserving its key properties, chiefly
lazy search and asymptotic optimality through convergence in probability. BFMT*
performs a two-source, lazy dynamic programming recursion over a set of
randomly-drawn samples, correspondingly generating two search trees: one in
cost-to-come space from the initial configuration and another in cost-to-go
space from the goal configuration. Numerical experiments illustrate the
advantages of BFMT* over its unidirectional counterpart, as well as a number of
other state-of-the-art planners.Comment: Accepted to the 2015 IEEE Intelligent Robotics and Systems Conference
in Hamburg, Germany. This submission represents the long version of the
conference manuscript, with additional proof details (Section IV) regarding
the asymptotic optimality of the BFMT* algorith
Evolutionary optimization algorithms for sunlight-based positioning sensor networks
The sunlight intensity-based global positioning system (SGPS) is able to geolocate outdoor objects by means of the sunlight
intensity detection. This paper presents the integration of SGPS into a sensor network in order to improve the overall accuracy
using evolutionary algorithms. Another contribution of the paper is to theoretically solve both global and relative positioning of
the sensors composing the network within the same framework without satellite-based GPS technology. Results show that this
approach is promising and has potential to be improved further
The Signs of Life Detector (SOLID): An Instrument to Detect Molecular Biosignatures on Mars
The case for life on Mars grows stronger. Investigations at Gale Crater by Curiosity have revealed fine-grained sedimentary rocks inferred to represent an ancient lake environment suited to support life. In addition, Curiosity tentatively found a heterogeneous distribution of organic carbon within these sediments, consistent with the detection of native organic C in Mars meteorites. Furthermore, modern potentially habitable environments have been recognized on Mars including the N. Polar region visited by Phoenix, gully features suggesting modern water flows, and RSLs that occur seasonally suggest liquid processes. The time is ripe for missions to Mars incorporating a search for biochemical evidence of life
Formation and Collapse of Quiescent Cloud Cores Induced by Dynamic Compressions
(Abridged) We present numerical hydrodynamical simulations of the formation,
evolution and gravitational collapse of isothermal molecular cloud cores. A
compressive wave is set up in a constant sub-Jeans density distribution of
radius r = 1 pc. As the wave travels through the simulation grid, a
shock-bounded spherical shell is formed. The inner shock of this shell reaches
and bounces off the center, leaving behind a central core with an initially
almost uniform density distribution, surrounded by an envelope consisting of
the material in the shock-bounded shell, with a power-law density profile that
at late times approaches a logarithmic slope of -2 even in non-collapsing
cases. The resulting density structure resembles a quiescent core of radius <
0.1 pc, with a Bonnor-Ebert-like (BE-like) profile, although it has significant
dynamical differences: it is initially non-self-gravitating and confined by the
ram pressure of the infalling material, and consequently, growing continuously
in mass and size. With the appropriate parameters, the core mass eventually
reaches an effective Jeans mass, at which time the core begins to collapse.
Thus, there is necessarily a time delay between the appearance of the core and
the onset of its collapse, but this is not due to the dissipation of its
internal turbulence as it is often believed. These results suggest that
pre-stellar cores may approximate Bonnor-Ebert structures which are however of
variable mass and may or may not experience gravitational collapse, in
qualitative agreement with the large observed frequency of cores with BE-like
profiles.Comment: Accepted for publication in ApJ. Associated mpeg files can be found
in http://www.astrosmo.unam.mx/~g.gomez/publica.htm
Prevalencia de diabesidad en España: depende de cómo se defina la obesidad
La obesidad representa la enfermedad metabólica más prevalente a nivel mundial, conllevando un aumento de la morbi-mortalidad y la consiguiente disminución en la esperanza de vida1. A pesar de la magnitud del problema y de la atención que recibe en las publicaciones científicas, la pandemia sigue creciendo de forma imparable. Según un estudio reciente llevado a cabo en 200 países, la prevalencia de la obesidad en el mundo se ha multiplicado por seis en los últimos 40 años4. La prevalencia de obesidad en Europa varía entre el 12 y el 26%5, rango dentro del cual se encuentran también las cifras en la población adulta española, entorno al 22%6. La obesidad se ha convertido en una de las principales causas de muerte, ya que constituye el principal factor de riesgo para una serie de enfermedades no transmisibles, en particular la diabetes tipo 2 (DT2)7,8. Esta estrecha relación llevó hace unos años a acuñar el término diabesidad, destacando el hecho de que la mayoría de las personas con DT2 tienen obesidad
Association of increased Visfatin/PBEF/NAMPT circulating concentrations and gene expression levels in peripheral blood cells with lipid metabolism and fatty liver in human morbid obesity
BACKGROUND AND AIMS: Nicotinamide phosphoribosyltransferase (NAMPT) is an
adipokine with physiological effects on the control of glucose homeostasis as
well as potentially involved in inflammation. The association of circulating
NAMPT concentrations with obesity has not been clearly established. The aim of
the present work was to evaluate the effect of obesity on circulating
concentrations and gene expression levels of NAMPT in human peripheral blood
cells (PBCs) as well as its involvement in inflammation, glucose and lipid
metabolism. METHODS AND RESULTS: Forty-four serum samples obtained from 14 lean
and 30 obese volunteers were used to analyse the circulating concentrations of
NAMPT. In addition, PBC, omental adipose tissue (OM) and liver biopsy samples
obtained from a subgroup of subjects were used to determine transcript levels of
NAMPT by Real-time PCR. Glucose and lipid profile as well as several inflammatory
factors and hepatic enzymes were analysed. NAMPT circulating concentrations
(P<0.01) and gene expression levels in PBC (P<0.05) were significantly increased
in obese patients as compared to lean subjects. Total-cholesterol (P=0.016),
HDL-cholesterol (P=0.036) and triglycerides (P=0.050) were significant and
independent determinants of circulating concentrations of NAMPT (P<0.01).
Moreover, a positive correlation (P<0.01) was found with the hepatic enzymes
alanine aminotransferase, aspartate aminotransferase, and
gamma-glutamyltransferase after BMI adjustment. CONCLUSION: Our work shows that
NAMPT circulating concentrations and mRNA expression levels in PBC are increased
in obese patients and that plasma NAMPT levels are related to inflammation, lipid
metabolism and hepatic enzymes suggesting a potential involvement in fatty liver
disease and in the obesity-associated inflammatory stat
The obestatin receptor (GPR39) is expressed in human adipose tissue and is down-regulated in obesity-associated type 2 diabetes mellitus
The G protein-coupled receptor 39 (GPR39) has recently been identified
as the receptor for obestatin, a peptidic hormone involved in energy homeostasis.
However, the expression levels of this receptor in human adipose tissue in
obesity and obesity-associated type 2 diabetes mellitus (T2DM) remain unknown.
Therefore, we evaluated the actual presence of GPR39 mRNA in human adipose tissue
and whether GPR39 expression levels are altered in obesity and obesity-associated
T2DM. DESIGN: Omental adipose tissue biopsies obtained from 15 women were used in
the study. Patients were classified as lean (body mass index 20.8 +/- 1.0
kg/m(2)), obese normoglycaemic (body mass index 48.4 +/- 2.1 kg/m(2)) and obese
T2DM patients (body mass index 52.6 +/- 4.9 kg/m(2)). Anthropometric measurements
and biochemical profiles were assessed for each subject. Real-time RT-PCR
analyses were performed to quantify transcript levels of GPR39 and adiponectin.
RESULTS: Obese T2DM patients exhibited significantly lower GPR39 expression
levels compared to lean (P = 0.016) and obese normoglycaemic subjects (P =
0.008), while no differences between lean and obese normoglycaemic patients were
observed. The mRNA expression levels of GPR39 were negatively correlated to
fasting glucose concentrations (r = -0.581, P = 0.023), while exhibiting a
positive correlation to adiponectin mRNA expression levels (r = 0.674, P =
0.006). CONCLUSION: GPR39 is expressed in human adipose tissue. The reduced
expression levels of GPR39 in omental adipose tissue observed in obese patients
with T2DM suggest an involvement of obestatin signalling in glucose homeostasis
and T2DM development
Expression of caveolin-1 in human adipose tissue is upregulated in obesity and obesity-associated type 2 diabetes mellitus and related to inflammation
Caveolin-1 (CAV-1) plays important roles in many aspects of cellular
biology, including vesicular transport, cholesterol homeostasis and signal
transduction. The aim of the present study was to explore gene expression levels
of CAV-1 in human adipose tissue in obesity and obesity-associated type 2
diabetes mellitus (T2DM) and to analyse its potential implication in the
inflammatory state associated with obesity. DESIGN AND METHODS: Visceral adipose
tissue (VAT) and subcutaneous adipose tissue (SAT) obtained from 15 females were
used in the study. Patients were classified as lean (BMI 20.8 +/- 1.0 kg/m(2)) or
obese (BMI 50.5 +/- 2.6 kg/m(2)). The obese group was further subclassified as
normoglycaemic (NG) or patients with T2DM. Anthropometric measurements as well as
circulating metabolites, hormones and adipokines were determined. Real-time
polymerase chain reaction (PCR) analyses were performed to quantify transcript
levels of CAV-1 and monocyte chemoattractant protein (MCP-1). RESULTS: The
presence of CAV-1 protein was detected in VAT and SAT by immunohistochemistry.
Both obese NG and with T2DM patients exhibited significantly higher CAV-1
expression levels in VAT and SAT compared with lean subjects (P < 0.05). No
differences between obese NG and T2DM patients were observed in VAT. However,
obese T2DM patients were found to have higher CAV-1 expression levels in SAT (P <
0.05) compared with obese NG patients. A significant correlation was found
between CAV-1 mRNA expression levels in VAT and different circulating
inflammatory markers such as sialic acid (SA) (P < 0.001) and fibrinogen (P <
0.001) as well as with MCP1 mRNA expression (P < 0.05). CONCLUSION: Our findings
show for the first time the upregulation of mRNA CAV-1 expression levels in VAT
and SAT of obese NG and obese T2DM patients compared with lean controls,
suggesting a role for CAV-1 in obesity and T2DM development. The association with
different inflammatory markers further suggests an implication of CAV-1 in the
low-grade inflammation accompanying obesity
Adiponectin-leptin Ratio is a Functional Biomarker of Adipose Tissue Inflammation
Obesity favors the development of cardiometabolic alterations such as type 2 diabetes (T2D) and the metabolic syndrome (MS). Obesity and the MS are distinguished by an increase in circulating leptin concentrations, in parallel to a drop in the levels of adiponectin. Consequently, the Adpn/Lep ratio has been suggested as a maker of dysfunctional adipose tissue. We aimed to investigate in humans (n = 292) the reliability of the Adpn/Lep ratio as a biomarker of adipose tissue dysfunction. We considered that an Adpn/Lep ratio of ≥1.0 can be considered normal, a ratio of ≥0.5 <1.0 suggests moderate-medium increased risk, and a ratio of <0.5 indicates a severe increase in cardiometabolic risk. Using these cut-offs, 5%, 54% and 48% of the lean, normoglycemic and without-MS subjects, respectively, fall within the group with an Adpn/Lep ratio below 0.5; while 89%, 86% and 90% of the obese, with T2D and with MS patients fall within the same group (p < 0.001). A significant negative correlation (r = -0.21, p = 0.005) between the Adpn/Lep ratio and serum amyloid A (SAA) concentrations, a marker of adipose tissue dysfunction, was found. We concluded that the Adpn/Lep ratio is a good indicator of a dysfunctional adipose tissue that may be a useful estimator of obesity- and MS-associated cardiometabolic risk, allowing the identification of a higher number of subjects at risk
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